NEMA is "National Electrical Manufacturers Association" and their standard
for motor mounts is commonly used in the industry to ensure that replacement
parts will fit and be readily available, and that motors from different mfgs
will be interchangeable. The NEMA number is related to the diameter of the
motor times 10. So a NEMA 23 motor is 2.3 inches around or down the side.

Please note: These figures are put together from multiple sources and
may or may not be right. Please let us know if there is an error.

Dimension in Inches (mm)

NEMA Motor Mounting Dimensions

NEMA 8

NEMA 11

NEMA 14

NEMA 17

NEMA 23

NEMA 34

NEMA 42

Motor Size (DD)

~0.8

~1.1

~1.4

~1.7

~2.3

~3.4

~4.2

a: Bolt Hole Distance (square)

0.630 (16)

0.905 (23)

1.024 (26)

1.220 (31)

1.854 (47.14)

2.744 (69.7)

3.500 (88.9)

b: Motor Shaft Diameter

0.157 (4)

0.197 (5)

0.197 (5)

0.197 (5)

0.250 (6.35)

0.375 (9.5)

0.625 (16)

c: Motor Shaft Length (max)

0.945

0.810

1.250

1.380

d: Pilot Diameter

0.590 (15)

0.866 (22)

0.866 (22)

0.866 (22)

1.500 (38.1)

2.875 (73)

2.186

e: Pilot Depth (max)

0.059 (1.5)

0.079 (2)

0.079 (2)

0.079 (2)

0.062 (1.6)

0.062 (1.6)

0.062 (1.6)

f: Bolt Hole Circle Diameter

1.725

2.625

3.875

4.950

g: Bolt Hole Size

0.118 (3)

0.157 (4)

0.157 (4)

4-40 UNC

0.195 (5)

0.218 (5.5)

0.281

Thanks to Neil (PICDude) for these excellent pictures!

The primary NEMA number specifies the position and size of the mounting face
as shown in the table above. The full NEMA standard also describes other
features of the motor. The full NEMA description of a stepper motor is written
as:
NEMA DDMMLLL-CCCIVVVSSSW, where:

DD is diameter (inches x 10). For square stepper motors, the length
of a side is used instead of the diameter.

MM is mount type code (inches x 10), include none, one or both of
these letter codes

"C" if there are holes tapped in the face of the motor

"D" If there is a flange on the back end of the motor with slots missed for
bolts to pass through

LLL is length (inches x 10), the "-" at this point separates mounting info from electric
characteristics.

CCC is phase current (amps x 10),

I is insulation class and defines the maximum allowable operating
temperature

Class A is 221'F

Class B is 266'F

Class F is 311'F

Class H is 356'F

VVV is phase voltage (rating x 10),

SSS steps per revolution,

W is a winding code.

A is two wires,

B is 3 wires,

C is 4 wires,

D is 5 wires,

E is 6 wires,

F is 8 wires

For example: a 3.4" diameter stepper motor with a flange that is 1.6 inches
long, has a phase current of 1.2 Amps, class B insulation, 5.3 phase voltage,
200 steps per revolution, and 8 wires is: NEMA 34D016-012B053200F

I have a query. I have a stepper motor square of 4.2 inches and length of approx. 6 inches. It has 4 (Four) wires, bipolar. apart from this I have no other information. I may be able to measure the coil resistance at the most. how do i determine the working voltage, current and watts? I need to choose a suitable drive for the motor.

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